Engine Idle Speed and Turbocharger Speed Control

ABSTRACT

Various methods are described for controlling engine operation for an engine having a turbocharger and direction injection. One example method includes performing at least a first and second injection during a cylinder cycle, the first injection generating a lean combustion and the second injection injected after combustion such that it exits the cylinder unburned into the exhaust upstream of a turbine of the turbocharger; and adjusting at least the first injection based on engine speed, where the at least first and second injection are performed responsive to turbocharger speed.

BACKGROUND AND SUMMARY

Engines may utilize turbocharging to increase power density and/orincrease engine fuel efficiency. However, during transient conditions,such as a driver request for increased engine output, turbochargerinertia and flow dynamics may result in “turbo lag.” Such lag may bereduced in some examples by reducing turbocharger size and weight,and/or taking various measures via engine control.

One control approach to address turbo lag uses a late fuel injectioninto lean diesel combustion to generate exhaust heat, therebymaintaining spin-up of the turbine of the turbocharger. Specifically,the late injection generates exhaust heat, which in turn increases thespeed of the turbine. Then, when a transient occurs, such as a requestfor an increase in engine output, the turbine is already spinning fastenough to provide the rapid increase in engine output.

However, the inventors herein have recognized some issues with the aboveapproach. In particular, in gasoline applications, the excess fuel usedto generate increased exhaust heat may degrade fuel efficiency. This isespecially true during idle, where significant spark reserve may be usedfor purposes of disturbance rejection. The combined fuel economydegradation of the excess injection, in addition to the fuel economydegradation due to the spark reserve, can lead to significant overallfuel economy losses. Additionally, in some applications, a lean exhaustair-fuel ratio may increase emissions.

The above issues may be at least partially addressed by a method forcontrolling engine operation for an engine having a turbocharger anddirection injection. The method may comprise: performing at least afirst and second injection during a cylinder cycle, the first injectiongenerating a lean combustion and the second injection injected aftercombustion such that it exits the cylinder unburned into the exhaustupstream of a turbine of the turbocharger; and adjusting at least thefirst injection based on engine speed, where said at least first andsecond injection are performed responsive to turbocharger speed.

In this way, less spark reserve may be used, at least in cylindersutilizing the first and second injection, since adjustments in the fuelinjection may be used to manage torque and speed disturbances. In otherwords, the lean combustion already has sufficient air to enableincreased combustion torque from increased fuel injection. However, theoverall air-fuel ratio can be maintained about stoichiometry via thesecond injection, while also providing increased heat to maintainturbocharger speed. In this way, increased fuel economy can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an example engine system includingtwin turbochargers.

FIGS. 2A, 3-4, 6-7 and 9 show high level flow charts depicting exampleapproaches for controlling engine and turbocharger operation.

FIGS. 2B-2C show example block diagram control systems for addressingidle speed control, turbocharger speed maintenance, and air-fuel ratiocontrol.

FIGS. 5 and 8 show prophetic examples of operation of severalembodiments.

DETAILED DESCRIPTION

FIG. 1 shows a schematic depiction of an example engine system 100including a multi-cylinder internal combustion engine 110 and twinturbochargers 120 and 130. As one non-limiting example, engine system100 can be included as part of a propulsion system for a passengervehicle. Also, while this example shows a twin turbocharger example, asingle turbocharger, or more than two turbines and/or compressors may beused.

Engine system 100 can receive intake air via intake passage 140. Intakepassage 140 can include an air filter 156. At least a portion of theintake air can be directed to a compression device or compressor 122 ofturbocharger 120 via a first branch of the intake passage 140 asindicated at 142 and at least a portion of the intake air can bedirected to a compressor 132 of turbocharger 130 via a second branch ofthe intake passage 140 as indicated at 144.

A first portion of the total intake air can be compressed via compressor122 where it may be supplied to intake manifold 160 via intake airpassage 146. Thus, intake passages 142 and 146 form a first branch ofthe engine's air intake system. Similarly, a second portion of the totalintake air can be compressed via compressor 132 where it may be suppliedto intake manifold 160 via intake air passage 148. Thus, intake passages144 and 148 form a second branch of the engine's air intake system. Asshown in FIG. 1, intake air from intake passages 146 and 148 can berecombined via a common intake passage 149 before reaching intakemanifold 160. In some examples, intake manifold 160 may include anintake manifold pressure sensor 182 and/or an intake manifoldtemperature sensor 183, each communicating with control system 190.Intake passage 149 can include an air cooler 154 and/or a throttle 158.The position of the throttle can be adjusted by the control system via athrottle actuator 157 communicatively coupled to control system 190. Asshown in FIG. 1, an anti-surge valve 152 may be provided to selectivelybypass turbochargers 120 and 130 via bypass passage 150. As one example,anti-surge valve 152 can open to enable flow through bypass passage 150where the intake air pressure of the combined air flow attains athreshold value.

Engine 110 may include a plurality of cylinders two of which are shownin FIG. 1 as 20A and 20B. Note that in some examples, engine 110 caninclude more than two cylinders such as 4, 5, 6, 8, 10 or morecylinders. Cylinders 20A and 20B may be identical in some examples andinclude identical components. As such, only cylinder 20A is described indetail. Cylinder 20A includes a combustion chamber 22A defined bycombustion chamber walls 24A. A piston 30A is disposed within combustionchamber 22A and is coupled to a crank shaft 34 via a crank arm 32A.Crank shaft 34 may include an engine speed sensor 181 that can identifythe rotational speed of crank shaft 34. Engine speed sensor 181 cancommunicate with control system 190 to enable a determination of enginespeed. Cylinder 20A can include a spark plug 70A for delivering anignition spark to combustion chamber 22A. However, in some examples,spark plug 70A may be omitted, for example, where engine 110 isconfigured to provide combustion via compression ignition. Combustionchamber 22A may include a fuel injector 60A, which in this example isconfigured as a direct in-cylinder fuel injector. However, in someexamples, fuel injector 60A can be configured as a port injector.

Cylinder 20A can further include at least one intake valve 40A actuatedvia an intake valve actuator 42A and at least one exhaust valve 50Aactuated via an exhaust valve actuator 52A. Cylinder 20A can include twoor more intake valves and/or two or more exhaust valves along withassociated valve actuators. In this particular example, actuators 42Aand 52A are configured as cam actuators, however, in other examples,electromagnetic valve actuators may be utilized. Intake valve actuator42A can be operated to open and close intake valve 40A to admit intakeair into combustion chamber 22A via intake passage 162 communicatingwith intake manifold 160. Similarly, exhaust valve actuator 52A can beoperated to open and close exhaust valve 50A to exhaust products ofcombustion from combustion chamber 22A into exhaust passage 166. In thisway, intake air may be supplied to combustion chamber 22A via intakepassage 162 and products of combustion may be exhausted from combustionchamber 22A via exhaust passage 166.

In one example, the system may include variable intake valve timingand/or variable exhaust valve timing. For example, the control mayadjust relative intake valve opening and/or closing timing based onengine operating conditions.

It should be appreciated that cylinder 20B or other cylinders of engine110 can include the same or similar components of cylinder 20A asdescribed above. Thus, intake air may be supplied to combustion chamber22B via intake passage 164 and products of combustion may be exhaustedfrom combustion chamber 22B via exhaust passage 168. Note that in someexamples a first bank of cylinders of engine 110 including cylinder 22Aas well as other cylinders can exhaust products of combustion via acommon exhaust passage 166 and a second bank of cylinders includingcylinder 22B as well as other cylinders can exhaust products ofcombustion via a common exhaust passage 168.

Products of combustion that are exhausted by engine 110 via exhaustpassage 166 can be directed through exhaust turbine 124 of turbocharger120, which in turn can provide mechanical work to compressor 122 viashaft 126 in order to provide compression to intake air as describedabove. Alternatively, some or all of the exhaust gases flowing throughexhaust passage 166 can bypass turbine 124 via turbine bypass passage123 as controlled by wastegate 128. The position of wastegate 128 may becontrolled by actuator 129 as directed by control system 190. As onenon-limiting example, control system 190 can adjust the position ofactuator 129 via a solenoid valve 121. In this particular example,solenoid valve 121 receives a pressure difference for facilitating theactuation of wastegate 128 via actuator 129 from the difference in airpressures between intake passage 142 arranged upstream of compressor 122and intake passage 149 arranged downstream of compressor 122. Asindicated by FIG. 1, control system 190 communicates with actuator 129via solenoid valve 121. However, it should be appreciated in otherexamples other suitable approaches for actuating wastegate 128 may beused.

Similarly, products of combustion that are exhausted by engine 110 viaexhaust passage 168 can be directed through exhaust turbine 134 ofturbocharger 130, which in turn can provide mechanical work tocompressor 132 via shaft 136 in order to provide compression to intakeair flowing through the second branch of the engine's intake system.Alternatively, some or all of the exhaust gases flowing through exhaustpassage 168 can bypass turbine 134 via turbine bypass passage 133 ascontrolled by wastegate 138. The position of wastegate 138 may becontrolled by actuator 139 as directed by control system 190. Theposition of wastegate 138 may be controlled by actuator 139 as directedby control system 190. As one non-limiting example, control system 190can adjust the position of actuator 139 via a solenoid valve 131. Inthis particular example, solenoid valve 131 receives a pressuredifference for facilitating the actuation of wastegate 138 via actuator139 from the difference in air pressures between intake passage 144arranged upstream of compressor 132 and intake passage 149 arrangeddownstream of compressor 132. As indicated by FIG. 1, control system 190communicates with actuator 139 via solenoid valve 131. However, itshould be appreciated that in other examples other suitable approachesfor actuating wastegate 138 may be used.

In some examples, exhaust turbines 124 and 134 may be configured asvariable geometry turbines, whereby associated actuators 125 and 135 maybe used to adjust the position of the turbine impeller blades to varythe level of energy that is obtained from the exhaust gas flow andimparted to their respective compressor. For example, the control systemcan be configured to independently vary the geometry of the exhaust gasturbines 124 and 134 via their respective actuators 125 and 135.

Products of combustion exhaust by one or more cylinders via exhaustpassage 166 can be directed to ambient via exhaust passage 170. Exhaustpassage 170 may include an exhaust aftertreatment device such ascatalyst 174, and one or more exhaust gas sensors (such as air-fuelratio sensors) indicated at 184 and 185, for example. Similarly,products of combustion exhaust by one or more cylinders via exhaustpassage 168 can be directed to ambient via exhaust passage 172. Exhaustpassage 172 may include an exhaust aftertreatment device such ascatalyst 176, and one or more exhaust gas sensors indicated at 186 and187, for example. Exhaust gas sensors 184, 185, 186, and/or 187 cancommunicate with control system 190.

Engine system 100 can include various other sensors. For example, atleast one of intake passages 140, 142, and 144 can include mass air flowsensor 180. A mass airflow sensor may include, as one example, a hotwire anemometer or other suitable device for measuring mass flow rate ofthe intake air. As one particular example, a first intake passage branch142 includes a mass air flow sensor 180 arranged upstream of compressor122 while a second intake passage branch 144 does not include a mass airflow sensor, although one may be added, if desired. As another example,mass air flow sensor 180 may be arranged along intake passage 146downstream of compressor 122. As yet another example, mass air flowsensor 180 may be arranged along intake passage 148 downstream ofcompressor 132. Regardless of the particular configuration, mass airflowsensor 180 can communicate with control system 190 as shown in FIG. 1.

Control system 190 can include one or more controllers configured tocommunicate with the various sensors and actuators described herein. Asone example, control system 190 can include at least one electroniccontroller comprising one or more of the following: an input/outputinterface for sending and receive electronic signals with the varioussensors and actuators, a central processing unit, memory such as randomaccessible memory (RAM), read-only memory (ROM), keep alive memory(KAM), each of which can communicate via a data bus. Control system 190may include a proportional-integral-derivative (PID) controller in someexamples. However, it should be appreciated that other suitablecontrollers may be used as can be appreciated by one skilled in the artin light of the present disclosure.

FIG. 1 further illustrates various operator interface elements, such asbrake pedal 192, gas pedal 194, and transmission gear selected 196, eachof which may transmit a corresponding signal to control system 190.Further, an example transmission 198 is shown, which may be coupled tothe engine and transmit various signals to, or receive signals from,control system 190.

Control system 190 can be configured to vary one or more operatingparameters of the engine on an individual cylinder basis. For example,the control system can adjust valve timing by utilizing a variable camtiming (VCT) actuator, spark timing by varying the time at which thespark signal is provided to the spark plug, and/or fuel injection timingand amount by varying the pulse width of the fuel injection signal thatis provided to the fuel injector by the control system as will also beappreciated in light of the present disclosure. Thus, the spark timing,valve timing, and fuel injection timing can be actuated by the controlsystem as will be described in greater detail herein.

Thus, FIG. 1 shows a non-limiting example of an engine system includingtwin turbochargers. In one example engine operation may be adjusted toincrease and/or maintain turbocharger speed during conditions in whichit would otherwise fall below a threshold valve resulting in increasedturbo lag during subsequent requests for increased engine output. In oneexample, the turbocharger speed can be increased by utilizing anadditional fuel injection pulse late in the combustion cycle, such asduring an exhaust stroke, late in the expansion stroke, and/or early inthe intake stroke (such as during valve overlap where boosted intakepressure forces flow through the cylinder and out into the exhaustmanifold), where the combustion air-fuel ratio was lean ofstoichiometry. In this way, excess air can react with injected fuel fromthe additional injection to generate exhaust heat and/or energy, andincrease work extracted by the turbocharger.

However, while such operation can reduce turbo lag and provide fastertorque increases, especially from idle conditions, such operation canalso increase overall fuel usage. During extended idle conditions, suchfuel usage may be significant to overall vehicle fuel economy. As such,in one embodiment, the turbocharger speed maintenance may be selectivelyused, or used to varying degrees, depending on operation conditions thatmay be indicative of an impending request to increase output. Forexample, release of a brake pedal may indicate an impending pedaltip-in, and thus trigger turbocharger speed maintenance at higher speedsin response thereto. Of course, other examples are also possible, suchas those described below herein with reference to FIG. 2A, and others.

Referring now to FIG. 2A, an example routine is described forcontrolling turbocharger speed maintenance. First, in 210, the routinereads operating conditions of the engine and/or vehicle, such asatmospheric conditions, temperatures, engine speed, requested engineoutput torque, desired engine speed, and others. Then, in 212, theroutine determines whether turbocharger speed maintenance is enabled,such as based on a time since engine start, degradation status of theturbocharger, exhaust temperature, etc. If so, the routine continues to214. If not, the routine continues to 216 to stop and/or disable anyadditional late injections.

In 214, the routine determines a minimum desired turbocharger speedbased on operating conditions. Alternatively, or additionally, theroutine may determine a minimum desired boost amount based on operatingconditions. Next, in 218, the routine determines whether turbochargerspeed is less than the minimum desired value (and/or whether the boostamount is less than the minimum desired boost amount). If not, again theroutine proceeds to 216. If so, the routine continues to 220 todetermine whether the brake pedal has been released and the engine iscurrently in an idle conditions (such as where engine speed iscontrolled to an idle speed), and the transmission is engaged in aforward gear. If so, this indicates that the driver may be about torequest an increase in engine output (e.g., releasing the brake todepress the gas pedal), and thus the routine continues to 222 to performturbocharger speed adjustment via additional direct fuel injection tomaintain or achieve the minimum desired turbocharger speed (and/orminimum boost amount), in combination with at least enleaning combustionair-fuel ratio (e.g., as generated by a first injection amount) toprovide excess air. Additionally, spark retard reserve can be reduced,as idle speed adjustments can be provided primarily via fuel injectionadjustments to the fuel injection amounts in order to reduce the fueleconomy penalty.

In one example, the amount of excess air may be coordinated with theamount of the additional injection, such that the overall exhaustair-fuel ratio is approximately stoichiometry. In this way, it may bepossible to address issues of turbo lag, at least under some conditions,while limiting increases in fuel usage. In other words, the lag inengine torque response to requests to increase torque may be addressedby injecting fuel into the exhaust system via direct cylinder injectionin order to keep the turbocharger spinning during tipped-out conditionsto reduce turbo lag on a subsequent tip-in. Additionally, by providingsufficiently lean combustion so that the excess air matches theadditional late fuel injection, an overall stiochiometric mixture can beprovided to downstream catalysts (e.g., 174/176).

Furthermore, while additional injection of fuel to provide increasedexhaust energy and increase turbocharger speed may have an effect onfuel economy, this may be offset at least in part by the adjustment ofthe lean combustion air-fuel ratio to maintain engine idle speed, andcorresponding reduce and/or eliminate the typical spark retard (e.g.,spark reserve) used to provide rapid idle speed feedback control. Inother words, higher frequency idle speed errors may be compensated byadjusting combustion air-fuel ratio (e.g., via adjustment of the amountof a first fuel injection), and similarly compensating (decreasing) theadditional late injection by a corresponding amount to maintainstoichiometry. Lower frequency errors may still be handled via airflowadjustment, such as via the throttle, boost pressure, etc. As such, thehigher frequency adjustment to the fuel injection amounts for idle speedcontrol would have a relatively negligible impact on turbocharger speedmaintenance. In addition to fuel economy benefits of reducing and/orremoving spark torque reserve, there may also be increased fuel economyby enabling operation with reduced pumping losses (potentially offset byincreased boost pressure).

Returning to FIG. 2A, if the answer to 220 is no, the routine continuesto 224 to determine whether the brake pedal was released during avehicle deceleration condition and while a forward gear was engaged. Ifso, this may also indicate an imminent driver tip-in, and thusturbocharger speed maintenance may be utilized in 222. Otherwise, theroutine continues to 226 to identify whether other conditions indicativeof an increased potential for a driver tip-in are present, and if so,continue to 222. Otherwise, the routine continues to 216.

In an alternative embodiment, the action of 222 may be performed duringdeceleration and/or idle conditions, unless the driver is currentlyengaging the brake pedal and not the accelerator pedal (e.g., brakeactuation is greater than a first threshold, and pedal actuation is lessthan a second threshold). Further, still other alternative approachesmay be used. For example, while FIG. 2A shows an example embodimentusing selective turbocharger speed maintenance, such turbocharger speedmaintenance can alternatively be used continuously during idle and/ordeceleration conditions.

One embodiment of a control diagram representation that relates to FIG.2A is shown in FIG. 2B. Specifically, FIG. 2B shows how the desiredvalues for air-fuel ratio (DES_AF), engine idle speed (DES_RPM), andturbine speed (DES_MIN_TS) drive adjustments in a first and second fuelinjection amounts, as well as throttle angle, in a coordinated way. Afirst controller 250 is shown for feedback control of exhaust mixtureair-fuel ratio (not necessarily combustion air-fuel ratio), where adesired air-fuel ratio (DES_AF) is compared to measured or estimatedair-fuel ratio (A/F) to form an error signal fed to the controller. Thecontroller, which may be a proportional, integral, and/or derivativecontroller, for example, then determines a total fuel injection amount(TOT_INJ), which may represent the total fuel delivered over a pluralityof injections for a given cylinder cycle. Specifically, the total fuelinjection may represent a total of the first injection event (used forcombustion and torque generation), and the second, late, injection usedfor heat generation in the exhaust. Note that other controller forms maybe used, such as linear, non-linear, etc.

Additionally, a second controller 252 is shown for feedback control ofengine speed, such as engine idle speed, where a desired engine speed(DES_RPM) is compared to measured or estimated engine speed (RPM) toform an error signal fed to the controller. The controller 252 thendetermines a first fuel injection amount (INJ_1), which may be deliveredduring the intake and/or compression stroke, and which combusts togenerate torque in the engine. Further, the block diagram illustrateshow the injection amount for the second injection (INJ_2) may then bedetermined by subtracting the first fuel injection amount from the totalfuel injection amount.

A third controller 254 is shown for feedback control of turbochargerspeed, where a minimum desired turbocharger speed (DES_MIN_TS) iscompared to measured or estimated turbocharger speed (TS) to form anerror signal fed first to a non-linear block 256, and then to thecontroller. Block 256 operates to form an on-sided controller where onlyunder-speed errors are corrected by the controller 254. The controller254 then determines a throttle angle adjustment, which is used alongwith a trim from block 258, to form a desired throttle angle (TA). Thetrim from block 258 is based on the amount of the second injection(INJ_2), and used to maintain a minimum reserve for dynamic range. Forexample, the control system may utilize longer term trim of throttleangle so that during engine idle speed error rejection, the secondinjection is less likely to fall below a minimum injection pulsewidth.

In this way, control of air-fuel ratio, idle speed, and turbochargerspeed can be coordinated when utilizing split injection operation, whilealso reducing likelihood of reaching range of authority limits in thecontrol actuators.

Continuing with the block diagram of FIG. 2B, it may result in variousoperation. For example, when controlling exhaust heat to maintainturbocharger speed above the minimum value, the system may increaseairflow while also increasing the relative size of the first to thesecond injection, and also increasing the total injection of fuel tomatch the increased airflow, thereby generating increased exhaust heat.Such operation may also be used to maintain idle speed and counteract adecrease in fuel-based lean combustion torque reserve. As anotherexample, the system may increase the relative size of the firstinjection to the second injection quickly to counteract sudden loads onthe engine or sudden drops in engine speed. However, lower frequencyadjustments may be handled by airflow adjustments to maintain sufficientheat for turbocharger speed control. Further still, while notillustrated in FIG. 2B, the number of cylinders utilizing a splitinjection may be adjusted to maintain turbocharger speed (e.g.,increasing the number of cylinders with split injection to increaseexhaust heat).

Referring now to FIG. 2C, another example block diagram is illustratedsimilar to that of FIG. 2B. Specifically, FIG. 2C shows how the desiredvalues for air-fuel ratio (DES_AF), engine idle speed (DES_RPM), torquereserve (DES_TQ_RESERVE) and turbine speed (DES_TRPM) drive adjustmentsin a first and second fuel injection amounts, as well as throttle angle,spark reserve, and air-fuel ratio in a coordinated way. A feedbackcontroller 260 and feedforward controller 262 are shown for control ofexhaust mixture air-fuel ratio (not necessarily combustion air-fuelratio), where a desired air-fuel ratio (DES_AF) is compared to measuredor estimated air-fuel ratio (A/F) to form an error signal fed tocontroller 260, and the desired air-fuel ratio is fed to controller 262.The controllers then determine a total fuel injection amount (TOT_INJ),which may represent the total fuel delivered over a plurality ofinjections for a given cylinder cycle. Specifically, the total fuelinjection may represent a total of the first injection event (used forcombustion and torque generation), and the second, late, injection usedfor heat generation in the exhaust. Note that various controller formsmay be used.

Additionally, a torque reserve controller 264 is shown for maintainingsufficient torque reserve to reject disturbances during idle speedcontrol. The controller receives the desired torque reserve, as well asa torque reserve adjustment (D_TQ_RESERVE) to partition the torquereserve between a commanded spark torque reserve (CMD_SPK_RESERVE), ifany, and a commanded combustion air-fuel ratio, which may also representthe air-fuel torque reserve, (CMD_COMB_A/F), if any. The controller maypartition the torque reserve based on operating conditions. For example,under some conditions, all of the reserve may be partitioned to thespark reserve, and under other conditions, all of the reserve may bepartitioned to the air-fuel reserve. As another example, the reserve maybe partitioned to both, in varying proportions, based on operatingconditions as described herein. Further still, controller 264 maycommand the system to first adjust the spark reserve before adjustingthe combustion air-fuel ratio and affecting the air-fuel reserve.

Based on the commanded air-fuel torque reserve, controller 266determines the first injection amount, which along with the totalinjection amount, determines the second injection amount.

Continuing with FIG. 2C, feedback controller 268 and feedforwardcontroller 270 provide control of engine speed, such as engine idlespeed, where a desired engine speed (DES_RPM) is compared to measured orestimated engine speed (RPM) to form an error signal fed to thecontroller. The controller 268 determines both the adjustment to thetorque reserve (D_TQ_RESERVE), as well as a change in airflow(D_AIRFLOW). The change in airflow is added to a desired airflow(DES_AIRFLOW) determined by controller 270 responsive to the desiredidle speed and the desired torque reserve. The summed airflow is thenfed to the throttle controller 272 to adjust the throttle angle toprovide the desired airflow (e.g., responsive to a mass airflow sensor).The change in airflow operates to drive the torque reserve adjustment toa small value (e.g., near zero), and thus back to the desired conditionsfor turbocharger speed control and idle speed control with sufficienttorque reserve.

Finally, controller 276 is shown for feedback control of turbochargerspeed, where minimum desired turbocharger speed (MIN_TS) is compared tomeasured or estimated turbocharger speed (TS) to form an error signalfed first to a non-linear block 274, and then to the controller 276,similar to that of FIG. 2B, to generate the desired combustion air-fuelratio (DES_COMB_A/F). Controller 276 may be a non-linear controller thatadjusts the desired combustion air-fuel ratio to maximum lean air-fuelratio for the engine operating conditions. However, other controlarchitectures may also be used.

In this way, control air-fuel ratio, idle speed, and turbocharger speedcan be coordinated when utilizing split injection operation, while alsoreducing likelihood of reaching range of authority limits in the controlactuators.

Referring now to FIG. 3, a routine is described for controllinginjection amounts of at least a first and second direct fuel injectionto the cylinder during turbocharger speed maintenance. In 310, theroutine determines whether late injection control is active, such asdetermined with regard to FIG. 2. If so, the routine continues to 312 todetermine an injection amount of a plurality of injection for a givencylinder cycle. In one example, the routine determine an amount of afirst and second direct injection, where the first injection isperformed either during an intake and/or compression stroke andcombusted to produce engine torque, and a second direct injection aftercombustion, which may be late during an exhaust stroke to provideunburned fuel to the exhaust. The desired first injection amount may bebased on a desired engine output (e.g., engine torque), while the secondinjection amount may be based on turbocharger speed, desiredturbocharger speed, etc., as noted herein.

Next, in 314, the routine determines timing of the injection amounts of312, such as relative to crank angle, piston position, intake valvetiming, exhaust valve timing, and/or other parameters. In one example,the timing may further be adjusted based on the injection amounts, toprovide delivery of the fuel at an appropriate time.

In 316, the routine then adjusts the injection amounts based on feedbackfrom exhaust air-fuel ratio sensors so that the exhaust air-fuel ratiois maintained at or oscillates about a desired value, and further basedon engine idle speed errors during idle speed control. For example, whenusing a first and second injection, the second injection amount may beadjusted based on both errors in the turbocharger speed, as well aserrors in air-fuel ratio. Further, the first injection amount may betemporarily adjusted based on idle speed errors during idle speedcontrol. In such a case, the second injection amount may be temporarilyadjusted by a corresponding amount to maintain air-fuel ratio. Ofcourse, alternative approaches may also be used. Thus, in one approach,a total injection amount may be set based on air-fuel ratio, and therelative amount of the first and second injections may be adjusted tobalance maintaining air-fuel ratio, turbocharger speed, and engineoutput torque (or idle speed during idle conditions). Further throttlecontrol can also be coordinated with such adjustments, as described infurther detail herein with regard to FIG. 4, for example.

Then, in 318, the routine determines a valve timing based on theinjection mode, amounts, and/or timings, and then in 320 the injectionsare performed as determined. For example, the valve timing and/or lift(e.g., intake valve opening/closing timing and/or exhaust valveopening/closing timing, intake valve lift, valve overlap, negative valveoverlap, etc.) may be adjusted based on whether directly injected fuelin the cylinder is exhausted for turbocharger speed maintenance is used.

Referring now to FIG. 4, a routine is described for coordinating lowerbandwidth throttle adjustments used to maintain sufficient controlauthority for idle speed control, while also maintaining turbochargerspeed. In one example, idle speed load rejection via adjustment of theinjection amount that is combusted in the cylinder—e.g., fuel-based idlespeed control with lean combustion—can operate at a higher bandwidth,throttle adjustments can be used to handle longer term, or steady state,corrections via airflow control. And, as already noted, the higherbandwidth adjustments can be trimmed out via the throttle on a timescale that limits any impact on turbo speed maintenance.

Turning now to FIG. 4, in 410, the routine determines idle speed error,if any, and corresponding control action based on the error and/or basedon feed forward parameters, such as power steering action, air/conditioncompressor operation, electrical loads, generator loads, etc. Forexample, a proportional, integral, and derivative control action may bedetermined. In another example, a non-linear controller may be used.Then, in 412, the routine determines whether late injection is active inone or more cylinders. If so, the routine continues to 414 to reducespark retard reserve in cylinders performing the late injection, andpossibly in all cylinders, even those without late injection (in theexample where some cylinders utilize late injection for turbochargerspeed maintenance, and others do not). If not, the routine continues to416, discussed further below.

From 414, the routine continues to 418 to determine whether the amountof control action of 410 is greater than a threshold. If so, the routinecontinues to 420 to adjust throttle opening and the relative amount of afirst and second injection to reduce idle speed error. Otherwise, theroutine continues to 416 where spark reserved is maintained in thecylinders, and the routine adjusts the throttle and spark advance toreduce idle speed error.

For example, in one embodiment, the routine may be providing a first andsecond injection amount, where the first amount produces a leancombustion and sufficient torque to maintain idle speed, while thesecond injection provides additional exhaust reductant to match excessair of combustion, and generate sufficient exhaust energy to maintainthe turbocharger speed at a target speed. However, upon the controlaction (or idle speed error) reaching a threshold value (e.g., due to asudden load on the engine, or due to an engine misfire, etc.), the firstamount may be increased, and the second injection amount decreased by acorresponding amount, to temporarily increase combustion torque (asexcess air is already present).

Further, if spark reserve is present in one or more (or all) cylinders,it may be used in combination with the adjustment to the first andsecond injection to provide the rapid torque increase in response to theidle error. For example, the fuel injection adjustment may be used incylinders using a first and second injection, while spark advancementcan be used in cylinders having a spark reserve without the late(second) injection. As another example, in response to the idle error ora sudden torque disturbance, the cylinders with spark reserve authoritymay first be adjusted to advance spark timing. Once the spark authoritywas exhausted, the first and second injection may be adjusted incylinders having a first and second injection. Such operation enablesthe split injection heat generation to continue for as long as possible,even during correction of most idle speed errors.

In another embodiment where both fuel injection adjustments and sparkreserve are used to control idle speed and turbocharger speed, the sparkreserve can be held until the control action reaches a second, greaterthreshold than the threshold of 418. In this way, the spark advance isused only after fuel injection adjustment reaches a control limit (suchas reducing the second injection to below the minimum pulse width,indicating that it is set to zero).

Referring now to FIG. 5, it illustrates a prophetic example ofoperation. The top graph shows engine idle speed and turbine speed overtime, the second graph shows the first and second injection amounts, andthe third graph shows throttle opening, and the bottom graph shows sparkangle. As shown, the idle speed is originally maintained at theset-point, and the turbine speed is maintained above a threshold value.

At t1 a disturbance causes a speed error in which idle speed drops. Inresponse thereto, the routine adjusts the first and second injectionamounts to increase the combusted fuel with lean combustion (althoughless lean due to increased fuel), while correspondingly decreasing thelate injection until the engine idle speed is again brought to theset-point value. However, as the fueling adjustment resulted in lesslate injection than needed to maintain turbocharger speed above thethreshold turbine speed, the throttle is adjusted at t2 to increasetotal airflow, and the fuel injection amounts correspondingly returnedto the desired amounts for turbocharger speed maintenance at t3 (e.g.,in the case where a load is placed and maintained on the enginerequiring an increase in output torque at steady state to maintain idlespeed at the set-point). Note that the third graph shows the injectionamounts relative to stoichiometry, and thus it does not show theincrease in both the first and second injection amounts that correspondto the increased airflow resulting from the throttle adjustments.

Referring now to FIG. 6, another routine is described for controllinginjections, throttle, and spark timing in coordination to maintain idlespeed and turbocharger speed when the fuelling adjustment reaches alimit value (in the example where some cylinders utilize a first andsecond injection, and other cylinders utilize spark reserve).Specifically, in 610, the routine determines whether late injection inone or more, but not all, cylinders is active. If so, the routinecontinues to 612 to determine control action based on idle speed errorbetween a desired idle speed and actual idle speed. Then, in 614, theroutine determines whether sufficient spark reserve authority is presentto meet the desired control action of 612. For example, if no sparkreserve is present, the routine continues to 616. Alternatively, if oneor more (or all) cylinder have some spark reserve, but stillinsufficient to meet the control action, the routine still continues to616 to utilize the available spark reserve, but then utilizes additionalcontrol actions in 618 where adjustment to the first and secondinjections are determined. Otherwise, when sufficient spark authority ispresent in 614, the routine continues to 620 to adjust the spark advancebased on the control action to control idle speed.

Continuing with FIG. 6, from 618, the routine continues to 622 todetermine whether the desired combustion air-fuel ratio generated viathe change in the first injection (for cylinders with late injection) isgreater than a threshold value. For example, combustion beyond aselected ratio (e.g., richer than 17:1) may be avoided. As such, in thiscase, the routine continues to 624 to adjust the throttle opening toincrease airflow and reduce the potential from the air-fuel ratioincreasing beyond the threshold.

Then, in 626, the routine, the routine determines whether the second(late) injection amount is less than a minimum pulsewidth (MIN_PW). Inone example, the minimum pulsewidth may represent a minimum pulsewidthunder which the injector can operate accurately under given operatingconditions.

If so, in 630, the routine adjusts injection amounts of the first amountto provide a stoichiometric combustion injection and sets the secondinjection amount to zero. Further, the routine adjusts throttle tomaintain idle speed, and increases spark reserve in one or morecylinders. Note the transition out of the mode using the second (late)injection may be managed as described herein with regard to FIG. 7, forexample. Otherwise, in 628, the routine provides the changed first andsecond injection amounts determined in 618 to reduce the speed error, incylinders with late injection.

Referring now to FIG. 7, a routine is described for controllingtransitions between a first operating mode including turbocharger speedmaintenance via late injection, and operation without such action.Specifically, in 710, the routine determines whether a transition intosplit injection operation for idle speed control and turbocharger speedmaintenance is present. If so, the routine continues to increase airflow(via throttle adjustment) in 712, further retard spark angle in 714, andthen advance spark angle while switching the injection mode in 716. Inthis way, engine torque can be maintained in 712 and 714 via coordinatedpreparation of countervailing effects of increased airflow and retardedspark angle. Then, upon activation of multiple injections (where thesecond injection does not produce engine torque), the effect of asmaller first injection (which is used to maintain air-fuel ratio) canbe counteracted via the advance of spark angle.

Alternatively, in 720, the routine determines whether a transition outof split injection operation for idle speed control and turbochargerspeed maintenance is present. If so, the routine continue to retardspark angle which changing injection modes in 722 to a single injection,and then further adjusts airflow and spark to achieve a desired sparkreserve in 724. In this way, engine torque and air-fuel ratio are againmaintained.

FIG. 8 illustrates another prophetic example of operation in whichcoordination of throttle, spark, and a first and second injection amountare used to control air-fuel ratio, idle speed, and turbocharger speedduring a first duration. Then, for a second duration that istransitioned into following the first duration, spark retard is usedwith only a single injection and throttle adjustment. Specifically, thetop graph shows engine idle speed and turbine speed over time, thesecond graph shows the first and second injection amounts, the thirdgraph shows throttle opening, and the bottom graph shows spark angle. Asshown, the idle speed is originally maintained at the set-point, and theturbine speed is maintained above a threshold value.

Similar to FIG. 5, a disturbance causes a speed error in which idlespeed drops. In response thereto, the routine adjusts the first andsecond injection amounts to increase the combusted fuel with leancombustion (although less lean due to increased fuel), whilecorrespondingly decreasing the late injection until the engine idlespeed is again brought to the set-point value to maintain air-fuelratio. However, as the fueling adjustment resulted in less lateinjection than needed to maintain turbocharger speed above the thresholdturbine speed, the throttle may be adjusted to increase total airflow,and the fuel injection amounts correspondingly returned to the desiredamounts for turbocharger speed maintenance (e.g., in the case where aload is placed and maintained on the engine requiring an increase inoutput torque at steady state to maintain idle speed at the set-point).Note that the third graph shows the injection amounts relative tostoichiometry, and thus it does not show the increase in both the firstand second injection amounts that correspond to the increased airflowresulting from the throttle adjustments.

At the transition, the second injection is ceased, and the firstinjection is correspondingly adjusted. However, to account for theresulting torque increase that would otherwise occur, spark angle isretarded. Such operation not only maintains torque through thetransition, but also provides a desired spark reserve that may be usedfor idle speed control as indicated to maintain speed in response to asecond disturbance.

Note that while the above example may refer to a first and second, late,injection, where the first is combusted and the second primarilyexhausted, more than two injections may be used. For example, twoinjections may be used before combustion, and third, late, injectionused that is exhausted. In any case the above examples, routines, anddescription should be understood to apply to various numbers ofinjections.

Referring now to FIG. 9, a routine is described for varying a number ofcylinders carrying out split injection for turbocharger speedmaintenance. First, in 910, the routine determines whether splitinjection is enabled for turbocharger speed maintenance. If so, theroutine continues to 912 to determine a minimum desired turbochargerspeed based on operating conditions, as described herein. Then, in 914,the routine determines engine idle load based on operating conditions.Next, in 916, the routine determines a number of cylinder in which toutilize additional (e.g., late) injection to control turbine speed basedon turbine operation and engine idle load. For example, the routine mayvary a number of cylinders with split injection in response toturbocharger speed dropping below the minimum value. Further, theroutine may vary such operation in response to engine load to maintainsufficient dynamic range with respect to actuators used to maintainengine idle speed as described herein. For example, feed forwardinformation from auxiliary loads may be used to select the number ofcylinders with split injection. Next, in 918, the routine adjusts anamount of late fuel injection in cylinders with late injection, andadjusts spark advance in cylinders without late injection to controlturbocharger speed above the minimum value. Further, additionaladjustments may also be used, such as adjustment of spark timing incylinders with late injection, exhaust gas recirculation, etc.

In this way, it may be possible to utilize variation in the number ofcylinders with split injection to better maintain turbocharger speedwhile balancing effects on engine idle speed disturbance rejection, fuelusage, and limitations on spark retard and lean combustion.

The specific routines described in the flowcharts and diagrams mayrepresent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps or functions illustrated may be performedin the sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments of the inventiondescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated steps orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, these figures graphically represent codeto be programmed into the computer readable storage medium in controller12.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense because numerous variations arepossible. The subject matter of the present disclosure includes allnovel and nonobvious combinations and subcombinations of the varioussystem and exhaust configurations, algorithms, and other features,functions, and/or properties disclosed herein. The following claimsparticularly point out certain combinations and subcombinations regardedas novel and nonobvious. These claims may refer to “an” element or “afirst” element or the equivalent thereof. Such claims should beunderstood to include incorporation of one or more such elements,neither requiring nor excluding two or more such elements. Othercombinations and subcombinations of the disclosed features, functions,elements, and/or properties may be claimed through amendment of thepresent claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method for controlling engine operation for an engine having aturbocharger and direction injection, the method comprising: performingat least a first and second injection during a cylinder cycle, the firstinjection generating a lean combustion and the second injection injectedafter combustion such that it exits the cylinder unburned into theexhaust upstream of a turbine of the turbocharger; and adjusting atleast the first injection based on engine speed, where said at leastfirst and second injection are performed responsive to turbochargerspeed.
 2. The method of claim 1, wherein the first injection is adjustedbased on engine idle speed to maintain idle speed, and during idleoperation, increasing the first injection amount in response toinadvertent speed drops, and correspondingly reducing the secondinjection to maintain an overall exhaust air-fuel ratio including thefirst and second injection about stoichiometry.
 3. The method of claim1, wherein an amount of the first and second injection are selected tomaintain increased turbine speed at least under selected conditions andincluding at least some idle operation, the method further comprisingadjusting throttle angle based on an amount of the first and secondinjections to maintain sufficient torque reserve with respect to thefirst injection relative to a maximum injection that corresponds tostoichiometric combustion.
 4. The method of claim 1 wherein the leancombustion is spark ignited, the method further comprising reducing aspark retard torque reserve during idle speed operation when performingthe at least first and second injection, where if the second injectionfalls below a threshold value, the second injection is disabled and thespark reserve is increased.
 5. A method for controlling engine operationfor an engine having a turbocharger and direction injection, the methodcomprising: performing at least a first and second injection during acylinder cycle, the first injection generating a lean combustion and thesecond injection injected after the first such that it at leastpartially exits the cylinder into the exhaust upstream of a turbine ofthe turbocharger, where said at least first and second injection areperformed responsive to turbocharger speed; and adjusting at least thefirst or second injection to maintain exhaust air-fuel ratio aboutstoichiometry.
 6. The method of claim 5, wherein the first injection isadjusted responsive to engine idle speed, and where if the firstinjection is increased in response to a decrease in engine idle speed,the second injection is decreased by a corresponding amount.
 7. Themethod of claim 5, wherein an amount of the first and second injectionare selected to maintain increased turbine speed at least under selectedconditions and including at least some idle operation, the methodfurther comprising adjusting throttle angle based on an amount of thefirst and second injections to maintain sufficient torque reserve withrespect to the first injection relative to a maximum injection thatcorresponds to stoichiometric combustion.
 8. The method of claim 5,wherein the lean combustion is spark ignited, the method furthercomprising reducing a spark retard reserve during idle speed operationwhen performing the at least first and second injection, where if thesecond injection falls below a threshold value, the second injection isdisabled and the spark reserve is increased.
 9. The method of claim 5where said adjusting is further responsive to exhaust air-fuel ratio,and where the second injection is adjusted responsive to the exhaustair-fuel ratio, the method further comprising adjusting a throttle angleresponsive to turbocharger speed.
 10. A method for controlling engineoperation for an engine having a turbocharger and direction injection,the method comprising: performing at least a first and second injectionduring a cylinder cycle, the first injection generating a leancombustion and the second injection injected after the first such thatit at least partially exits the cylinder into the exhaust upstream of aturbine of the turbocharger, where said at least first and secondinjection are performed responsive to turbocharger speed; and duringselected idle conditions: adjusting at least the first injection tomaintain engine idle speed; adjusting at least the second injection tomaintain exhaust air-fuel ratio about stoichiometry; and adjustingairflow to maintain turbocharger speed above a threshold value.
 11. Themethod of claim 10, where the adjustments of the first injection, secondinjection, and airflow are coordinated with respect to one another, andsaid selected idle conditions are identified by conditions indicative ofa transient torque increasing condition.
 12. The method of claim 10,where if the second injection is decreased so that the injection resultsin a command signal to the injector below a minimum pulse width, thesecond injection is disabled and a spark reserve is increased inresponse thereto.
 13. The method of claim 10, wherein an amount of thefirst and second injection are selected to maintain increased turbinespeed, the method further comprising adjusting throttle angle based onan amount of the first and second injections to maintain sufficienttorque reserve with respect to the first injection relative to a maximuminjection that corresponds to stoichiometric combustion.
 14. The methodof claim 10, wherein the lean combustion is spark ignited, the methodfurther comprising reducing a spark retard reserve during the selectedidle speed conditions compared with idle speed conditions using only asingle direct injection.
 15. The method of claim 10, where the leancombustion is spark ignited, and the exhaust air-fuel ratio oscillatedabout stoichoimetry, where the performing is carried out during a firstidle speed control condition, the method further comprising adjusting atleast spark timing to maintain engine idle speed during a second idlespeed control condition.
 16. A method for controlling engine operationfor an engine having a turbocharger and direction injection, the methodcomprising: performing at least a first and second injection during acylinder cycle with at least some spark reserve, the first injectiongenerating a lean combustion and the second injection injected after thefirst such that it at least partially exits the cylinder into theexhaust upstream of a turbine of the turbocharger, where said at leastfirst and second injection are performed responsive to turbochargerspeed to maintain turbine speed above a threshold value; and in responseto an idle speed error or external load application, first advancingspark angle, and then increasing at least the first injection, tomaintain idle speed.
 17. The method of claim 16, further comprising inresponse to the idle speed error or external load application,correspondingly decreasing the second injection in response to theincrease in the first injection to maintain exhaust air-fuel ratio. 18.The method of claim 16, wherein an amount of the first and secondinjection are selected to maintain increased turbine speed at leastunder selected conditions and including at least some idle operation,the method further comprising adjusting throttle angle based on anamount of the first and second injections to maintain sufficient torquereserve with respect to the first injection relative to a maximuminjection that corresponds to stoichiometric combustion.
 19. The methodof claim 16 wherein the lean combustion is spark ignited, the methodfurther comprising increasing the spark retard reserve during idle speedoperation when performing only a single injection.
 20. A method forcontrolling engine operation for an engine having a turbocharger anddirection injection, the method comprising: operating in a first idlespeed mode during a first idle speed control condition, the first modeincluding at least a first and second injection during a cylinder cycle,the first injection generating a lean combustion and the secondinjection injected after combustion such that it exits the cylinderunburned into the exhaust upstream of a turbine of the turbocharger,where the at least first and second injection are performed responsiveto turbocharger speed, the first mode further including adjusting atleast the first injection based on engine speed; and operating in asecond idle speed mode during a second idle speed control condition, thesecond mode including only a single injection and a spark reserve, whereat least spark angle is adjusted based on engine speed to maintain idlespeed; and transitioning between the first and second modes based ondriver inputs, and when transitioning into the first mode, spark timingis advanced while splitting the single injection into the first andsecond injection, and when transitioning into the second mode, sparktiming is retarded while combining the first and second injections intothe single injection.
 21. The method of claim 20, wherein the first modeincludes at least some spark reserve, but less than the reserve in thesecond mode, and where during the second mode, throttle angle is furtheradjusted based on engine speed.
 22. The method of claim 20, whereinduring the first mode, the first injection is adjusted based on engineidle speed to maintain idle speed, including increasing the firstinjection amount in response to inadvertent speed drops, andcorrespondingly reducing the second injection to maintain an overallexhaust air-fuel ratio including the first and second injection aboutstoichiometry.
 23. The method of claim 20, wherein during the first modean amount of the first and second injection are selected to maintainincreased turbine speed at least under selected conditions.
 24. Themethod of claim 20 wherein the lean combustion is spark ignited.